This invention relates generally to the field of controlled path motion for manipulators. Such manipulators may carry a tool, such as a welding electrode requiring manipulation to a series of points along a workpiece. A typical manipulator of that type may be constructed as generally described in Holmes et al U.S. Pat. No. 4,598,380. Such a manipulator may be computer controlled to move a tool along straight line paths between a series of reference points, the coordinates of which are input to the computer during a teaching phase. Teaching of the reference points may be carried out as generally taught by Corwin, Jr. et al U.S. Pat. No. 3,920,972, and path control may be carried out as taught in Hohn U.S. Pat. No. 3,909,600 or in Magnuson U.S. Pat. No. 4,506,335.
In some applications, such as welding, it is necessary to cause movement of a tool along a circular arc or other curved path. Prior art methods of tool manipulation require that a large number of reference points be taught to the computer in order to achieve tool movement along a reasonably smooth path. Such teaching requires that the manipulator be correctly oriented as well as positioned at each such point.
It is therefore seen that there is a need for an improved method for moving a tool along a curved path. It is desired that the teaching phase for such manipulation require movement of the tool to only a relatively few points, that the work plane not be constrained to a horizontal or vertical orientation and that the tool maintain a desired process orientation as it moves along its working path.